Adjustable band resistor



June 30, 1942. A. A. FOLEY 2,288,235

ADJUSTABLE BAND RESISTOR Filed Sept. 14, 1940 INVENTOR .Hndrew .H. F0167@MLLM/ (MW! ATTO EYS Patented June 30, 1942 ADJUSTABLE BAND RESISTORAndrew A; Foley, Camden, N. 1., assignor to International ResistanceCompany, Philadelphia, Pa., a corporation of Delaware ApplicationSeptember 14, 1940, Serial No. 356,720

Claims.

This invention relates to the manufacture of adjustable electricalresistors and more particularly to an improved adjustable contact deviceand terminal for such a resistor.

One of the objects of this invention is to provide a terminal structurefor a resistor or the like which will be simple, practical and durable.Another object is to provide a construction of the above character whichmay be made from inexpensive materials and at low labor cost. Anotherobject is to provide a terminal structure capable of easy adjustment todifferent positions along the length of a resistor unit. Another objectis to provide a structure of the above character which may be easilysecured in any allotted position on the resistor at the same timeassuring an adequate electrical connection with that portion of theresistor. Other objects will be in part obvious and in part pointed outhereinafter.

The invention accordingly consists in the features of construction,combinations of elements, and arrangements of parts as will beexemplified in the structure to be hereinafter described and the scopeof the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of the variouspossible embodiments of my invention:

Figure 1 is a general view of an adjustable resistor;

Figure 2 is an enlarged vertical section taken along the line 2-2 ofFigure 1;

Figure 3 is an exploded perspective view of certain of the parts of theclamping band and contact support; and

Figure 4 is a top plan view on an enlarged scale of the clamping band.

This application is a continuation-in-part of my copending applicationSerial No. 323,098, filed March 9, 1940, entitled Adjustable bandresistor.

As conducive to a clearer understanding of this invention it might herebe pointed out that it is desirable under certain circumstances toprovide an adjustable terminal for an adjustable resistor or the like.Often it is convenient to tap such a resistor and the exact point ofsuch tap cannot be determined until installation, thus making itnecessary to provide some structure which may be easily adjusted todifferent positions along the length of an adjustable resistor. In thepast, such adjustable terminal structures have been open to certainoperating deficiencies making them inconvenient to use and unreliable inoperation. Many of these adjustable terminals are characterized by aband portion extending about the body of the resistor, and provision fortightening this band. However, the tightening of the band to fix it atany given location on the resistor often causes distortion whichmayresuit in an unstable electrical connection between the terminal andthe resistor. Another object of this invention is to provide aconstruction in which the above-mentioned difficulties as well as manyothers are successfully and efficiently overcome.

Referring to the drawing, and particularly to Figures 1 and 2, there isshown a resistor preferably comprising a tubular ceramic core i havingresistance wire 2 helically wound thereon and covered by a suitableinsulating and mechanically protective coating 3 such as cement,vitreous enamel, or the like. As shown in Figure 1, the coating 3 isprovided with a narrow longitudinal slot 4 forming an exposed portion 5of the resistance wire 2. At its ends the resistance wire 2 iselectrically connected to the fixed terminals 6, whereby the resistormay be connected to and incorporated in an electrical circuit.

Intermediate the fixed terminals 6 there is an adjustable contact deviceand terminal, general- 1y designated by the numeral 8 and comprising ametal band 9 which passes around the resistor and, as shown in Figure 2,terminates in two downwardly extending arms I!) and H. Arm I0 isprovided with a right angle lip or projection I! which bears against thearm ii as shown. To hold the arms of the clamping band 9 together and totighten the band on the resistor, there is provided between lip l2 andthe resistor a screw l3. which passes through a hole in the arm l0 andthreads into a built up section it of arm ii.

Arms l0 and II, lip l2, and screw it cooperate to reduce the possibilityof distortion of band 9 about the resistor during tightening of thescrew; lip l2 acts as a fulcrum and the arms l0 and II act as levers intransmitting the pressure exerted by the screw iii to the main circularportion of the clamping band 9, and consequently the force tending totighten the band on the resistor is always exerted in a directionapproximately tangential to the surface of the resistor. Thus, with thisconstruction, there is appreciably less chance of distorting the bandwhen the screw I3 is tightened.

At its lower end, the arm II is provided with an electrical terminalcomprising a bolt H which passes through a hole IS in the arm, and isheld in place by a nut ii. The end of a wire or other electricalconductor leading to an external circuit may be held between two washersi8 carried on the bolt l5, and held in place by a lock nut i9.

Electrical contact with the resistance wire 2 is effected through aresilient metal strip 20 secured at one end, preferably by spot welding,to the outer surface of metal band 9. At its other end, strip 20supports a contact button or point II also preferably afllxed by spotwelding and made of a non-corrosive conductive material such as silver.The contact button passes through an oval aperture 22 (see Figure 3) inthe band 9 to engage the resistance wire 2 and exerts on the exposedportion 5 thereof radial pressure, the magnitude of which is determinednot by the tightness of the metal band 9 about the resistor, but by thetension of resilient strip 20. Thus the pressure which the contactbutton exerts on the resistance wire 2 is substantially independent ofthe tightness of the clamping band 9. As shown in Figures 2 and 3, thestrip at its contact supporting end may be slightly flattened to providesubstantially perpendicular pressure against resistance wire 2 and aconsequent better electrical connection therebetween.

From the above description, it is apparent that in the present inventionthe pressure exerted by the contactor on the resistance wire isdetermined by the resilient characteristics of the strip 20. as to breakor distort the resistance wire; nor too small, so as to cause inadequateelectrical connection. Consequently the efiiciency of the resultantelectrical connection is not dependent upon the skill of theinstallerovertightening or undertightening of the clamping band willhave substantially no effect on the pressure which the contact exerts.Moreover, the tendency of the clamping band to distort about theresistor will be appreciably reduced.

In certain instances, it is desirable to place the clamping band uponthe resistor by spreading arms I0 and H and then passing the resistorbetween them. When the arms are spread, deformation of the band takesplace, and, in order to prevent such deformation from disturbing therelative positions of strip 20 and band 9, a pair of notches and 26(Figures 3 and 4) are cut in the edges of the band preferably at the topthereof. The band is weakened by these notches a greater amount than byaperture 22, and thus, when the arms are spread, the band is deformed orbends in that portion of the band between notches 25 and 26. Thus, whenthe band is placed upon the resistor by spreading arms i0 and ii, thedeformation thereof is concentrated at a given point, and accordingly,the relative positions held by strip 20 and band 9 before the Thus thispressure will not be too large, so

band is bent are maintained during the placing the clamping band uponthe resistor to assure a good electrical connection between button 2|and wire 2.

Accordingly, it will be seen that I have provided a thoroughlypractical. terminal structure for a resistor or the like in which theseveral objects hereinabove referred to, as well as many others, aresuccessfully and practically accomplished.

As many possible embodiments may be made of the above invention and asmany changes might be made in the embodiment above set forth, it is tobe understood that all matter hereinbefore set forth or shown in theaccompanying drawing is to be interpreted as illustrative and not in alimiting sense.

I claim:

1. In resistor construction, in combination, a resistor, a bendableclamping band. of substantially the same general shape as the crosssection of said resistor, said clamping band when applied to saidresistor fitting firmly thereabout and exerting pressure thereon, and acontact member resiliently mounted on said clamping band, the contactingportion of said contact member resiliently engaging the resistance ele--ment of said resistor, whereby the contacting portion of said contactmember exerts a pressure on said resistance elementsubstantiallyindependent of the pressure exerted on said resistor by said clampingband.

2. In resistor construction, in combination, a

resistor, a bendable clamping band of substantially the same generalshape as the cross section of said resistor, said clamping band whenapplied to said resistor fitting firmly thereabout and exerting pressurethereon, a resilient strip anchored at one end to said clamping band,and a contact normally in engagement with the resistance element of saidresistor mounted on the other end of said strip, said resilient stripforming the only connection between said clamping band and said contact,whereby said contact exerts a pressure on said resistance elementsubstantially independent of the pressure exerted by said clamping bandon said resistor.

3. In resistor construction, in combination, a resistor, a bendableclamping band of substantially the same generalshape as the crosssection of said resistor, said clamping band when applied to saidresistor fitting firmly thereabout and exerting pressure thereon, saidclamping band being adjustable longitudinally of said resistor andhaving an aperture formed therein, a resilient strip mounted on theoutside of said clamping band and having one end anchored thereon, and acontact normally engaging the resistance element of said resistorthrough said aperture mounted on the other end of said strip, saidresilient strip forming the only connection between said band and saidcontact, whereby said contact exerts a. pressure on the resistanceelement of said resistor substantially independent of the pressureexerted by said clamping band on said resistor.

4. An adjustable resistor comprising, in combination, a core, aresistance wire wound thereon, a non-conductive coating covering saidresistance wire, said coating having a longitudinal slot exposing aportion of said wire, a metallic clamping band passing around saidresistor and terminating in two outwardly extending arms, a contactmounted on said band resiliently engaging said exposed portion of saidresistance wire, a lip formed on one of said arms and engaging the otherof said arms, adjustable tightening means for said clamping bandinterposed between said lip and said resistor, said tightening means andsaid lip cooperating with said arms to prevent appreciable distortion ofsaid hand during the tightening thereof.

5. In resistor construction, in combination, an elongated resistor, ametal clamping band extending around said resistor, said band beingadjustable longitudinally of said resistor and having an aperture formedtherein, an electrical contact member resiliently mounted on the outsideof said band and contacting the resistance element of said resistorthrough said aperture, and means securing the ends of said band togetherto hold said band in said position on said resistor, said band' having acut-out portion spaced from said contact member and adapted to weakensaid band a greater amount than said aperture does, whereby, when theends of said band are separated, deformation of said band takes place atthe point in said band weakened by said cut-out portion.

ANDREW A. FOLEY.

v CERTIFICATE'OF CORRECTION. Patent No; 2,2 ,255. June 50, 19 2.

' ANDREWA. FOLEY.

It is'hereby certified that error appears in the printed specificationof the above numbered patent requiring correcti on'as follows: Page 2,first column, li 1 ,9, after "placing" insert --of-'-; and secondcolumn,-l1ne 32, claim 5, for thereon' ad -thereto-; and thatth'e,sa;1.d LettersPatent should-be read. with this correction thereinthat the some may conform to the record of the ease in the PatentOffice.

Signed and. sealed thie let-day ofDecember, A. D. 1911.2.

; Henry Van Arsdal e,

(Seal) Acting Commissioner of Patents.

v CERTIFICATE'OF CORRECTION. Patent No. 2,288,255. June 50, 19+2.

' I ANDREWA. FOLEY.

It j g-hereby certified that error appears in the printed specificationI bf the above numbered patent requiring correcti on-as follows: Page 2,first column, l 1 9, after placing insert .-.-pf--; and secondcoluinn-,-l1ne 52,

claim 5, for "thereon" re'ad -there to--; and that th'esaid LettersPatent shduldbe read with this correction thqarein that th snie may confomto the record of the case in the Patent Office Signed and sealea glst'daj bfDecembemA. D. 191m.

- Henry Van ArsdaIe (Seal) Acting Commissioner of Patents.

